[SYMBOL] [A] [B] [C] [D] [E] [F] [G] [H] [I] [J] [K] [L] [M] [N] [O] [P] [Q] [R] [S] [T] [U] [V] [W] [X] [Y] [Z] X command (ex)  x command (sed)  X Window System  xargs command  XDR (eXternal Data Representation)  XFS (Extensible Filesystem)  Ximian Red Carpet  Xinerama  2nd  xinetd command  xit command (ex)  xor command (gawk)